1. Field of the Invention
The present invention relates to a filter adapted to, for example, remove ghost signals or multipath signals from a video signal, and more particularly, to an input-weighted transversal filter for performing filtering arithmetic processing on digital signal, such as a video signal, an audio signal, etc., in real time.
2. Description of the Related Art
FIG. 6 illustrates a conventional 6 -tap input-weighted transversal filter. To an input terminal 1 of the transversal filter is applied a time-series input signal {X(i)} which has been sampled at regular intervals T. The input signal {X(i)} is applied to six coefficient multipliers 10 to 15. Each of the multipliers 10 to 15 is constructed mainly from a multiplier. The multipliers 10 to 14 multiply the input signal {X(i)} by coefficients C0 to C4, respectively, and feed the results of the multiplication to adders 20 to 24, respectively. The multiplier 15 multiples the input signal by the coefficient C5 and then applies the output to a delay element 34 for introducing a time delay T in a signal.
The delay elements 30 to 34 are connected in cascade with each of the adders 21 to 24 interposed between adjoining delay elements. An input of the adder 20 is connected to the delay element 30. An output signal of the adder 20 is coupled to an output terminal 2 via a delay element 4. The delay elements 30 to 34 are driven by a clock signal CK.
The output signal {Y(i)} of the adder 20 of the transversal filter is represented by ##EQU1## The signal {Y(i)} is held for a time interval T by the delay element 4 to provide the final output signal of the transversal filter.
FIG. 7 is a block diagram illustrating an actual hardware configuration of the transversal filter. This transversal filter is composed of six tap arithmetic units 41.
FIG. 8 illustrates an arrangement of the tap arithmetic unit 41 of FIG. 7. In this FIGURE, a delay element 44 comprised of, for example, a shift register is interposed between a pipeline type multiplier 42 and an adder 43 which serve as the arithmetic unit. The delay element 44 is provided in view of the arithmetic operation speed of the pipeline multiplier 42. In the tap arithmetic unit 41, the input signal {(X(i)} and the coefficient Ci is multiplied and the result of the multiplication is delayed by the delay element 44 in synchronization with the clock signal CK1. The adder 43 adds an output signal {Y(i-1)} output from the preceding tap arithmetic unit not shown to the signal output from the delay element 44. The result of the addition is delayed by a given time by the delay element 45 to yield the signal {Y(i)}.
FIGS. 9A, 9B and 9C are a timing chart of the operation of the transversal filter of FIG. 7. The output signals of the tap arithmetic units are also indicated.
FIG. 10 illustrates an example of the pipeline multiplier 42 of FIG. 8. In this pipeline multiplier 42, the input signal {X(i)} is 5 bits in length and the coefficient Ci is 5 bits in length.
In FIG. 10, the pipeline multiplier 42 is constructed from a multiplier 42a, a pipeline delay circuit 42b and an adder 42c. The multiplier 42a is constructed from half-adders (HA) and full-adders (FA) to multiply the input signal {X(i)} and the coefficients. The delay circuit 42b is constructed from shift registers R20 to R32 to delay output signals of the multiplier 42a in response to the clock signal CK. The adder 42c comprises a half-adder H15 and full-adders F37 to F39.
The tap arithmetic unit 41 constructed as above includes the delay circuit 42b within the pipeline multiplier 42 and the delay element 44 for delaying the output signal of the multiplier 42. Thus, in the integrated-circuit version of the tap arithmetic unit, the delay elements will occupy a large area of the integrated-circuit chip because there is a need for many shift registers, increasing manufacturing cost.
Moreover, in the cascade-connection of transversal filters, the delay amount of the entire system will increase because the number of shift registers is large. To circumvent this, unnecessary full-adders are required in the succeeding transversal filters.